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Register a new userComplex Structure of the Eastern Lobe of the Pictor A Radio Galaxy: Spectral Analysis and X-ray/Radio Correlations
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Here we present detailed analysis of the distinct X-ray emission features present within the Eastern radio lobe of the Pictor A galaxy, around the jet termination region, utilising the data obtained from the Chandra X-ray Observatory. Various emission features have been selected for the study based on their enhanced X-ray surface brightness, including five sources that appear point-like, as well as three extended regions, one characterised by a filamentary morphology. For those, we perform a basic spectral analysis within the 0.5-7keV range. We also investigate various correlations between the X-ray emission features and the non-thermal radio emission, utilising the high-resolution radio maps from the Very Large Array at GHz frequencies. The main novel findings following from our analysis, regard the newly recognized bright X-ray filament located upstream of the jet termination region, extending for at least thirty kiloparsec (projected), and inclined with respect to the jet axis. For this feature, we observe a clear anti-correlation between the X-ray surface brightness and the polarized radio intensity, as well as a decrease in the radio rotation measure with respect to the surroundings. We speculate on the nature of the filament, in particular addressing a possibility that it is related to the presence of a hot X-ray emitting thermal gas, only partly mixed with the non-thermal radio/X-ray emitting electrons within the lobe, combined with the reversals in the lobes net magnetic field.
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We report the results of monitoring of the radio galaxy 3C 120 with the Neil Gehrels Swift Observatory, Very Long Baseline Array, and Metsahovi Radio Observatory. The UV-optical continuum spectrum and R-band polarization can be explained by a superposition of an inverted-spectrum source with a synchrotron component containing a disordered magnetic field. The UV-optical and X-ray light curves include dips and flares, while several superluminal knots appear in the parsec-scale jet. The recovery time of the second dip was longer at UV-optical wavelengths, in conflict with a model in which the inner accretion disk (AD) is disrupted during a dip and then refilled from outer to inner radii. We favor an alternative scenario in which occasional polar alignments of the magnetic field in the disk and corona cause the flux dips and formation of shocks in the jet. Similar to observations of Seyfert galaxies, intra-band time lags of flux variations are longer than predicted by the standard AD model. This suggests that scattering or some other reprocessing occurs. The 37 GHz light curve is well correlated with the optical-UV variations, with a ~20-day delay. A radio flare in the jet occurred in a superluminal knot 0.14 milliarcseconds downstream of the 43 GHz core, which places the site of the preceding X-ray/UV/optical flare within the core 0.5-1.3 pc from the black hole. The inverted UV-optical flare spectrum can be explained by a nearly mono-energetic electron distribution with energy similar to the minimum energy inferred in the TeV gamma-ray emitting regions of some BL Lacertae objects.
We present optical integral field spectroscopy of the inner $2.5 times 3.4$ kpc$^2$ of the broad-line radio galaxy Pictor A, at a spatial resolution of $approx 400$ pc. Line emission is observed over the whole field-of-view, being strongest at the nucleus and in an elongated linear feature (ELF) crossing the nucleus from the south-west to the north-east along PA $sim 70^circ$. Although the broad double-peaked H$alpha$ line and the [OI]6300/H$alpha$ and [SII]6717+31/H$alpha$ ratios are typical of AGNs, the [NII]6584/H$alpha$ ratio (0.15 - 0.25) is unusually low. We suggest that this is due to the unusually low metallicity of the gas. Centroid velocity maps show mostly blueshifts to the south and redshifts to the north of the nucleus, but the velocity field is not well fitted by a rotation model. Velocity dispersions are low (< 100 km s$^{-1}$) along the ELF, ruling out a jet-cloud interaction as the origin of this structure. The ELF shows both blueshifts and redshifts in channel maps, suggesting that it is close to the plane of the sky. The ELF is evidently photoionized by the AGN, but its kinematics and inferred low metallicity suggest that this structure may have originated in a past merger event with another galaxy. We suggest that the gas acquired in this interaction may be feeding the ELF.
Mid-infrared properties are reported of the west hot spot of the radio galaxy Pictor A with the Wide-field Infrared Survey Explorer (WISE). The mid-infrared counterpart to the hot spot, WISE J051926.26-454554.1, is listed in the AllWISE source catalog. The source was detected in all the four WISE photometric bands. A comparison between the WISE and radio images reinforces the physical association of the wise source to the hot spot. The WISE flux density of the source was carefully evaluated. A close investigation of the multi-wavelength synchrotron spectral energy distribution from the object reveals a mid-infrared excess at the wavelength of $lambda=22$ $mu$m with a statistical significance of $4.8 sigma$ over the simple power-law extrapolation from the synchrotron radio spectrum. The excess is reinforced by single and double cutoff power-law modeling of the radio-to-optical spectral energy distribution. The synchrotron cutoff frequency of the main and excess components was evaluated as $7.1 times 10^{14}$ Hz and $5.5 times 10^{13}$ Hz, respectively. From the cutoff frequency, the magnetic field of the emission region was constrained as a function of the region size. In order to interpret the excess component, an electron population different from the main one dominating the observed radio spectrum is necessary. The excess emission is proposed to originate in a sub structure within the hot spot, in which the magnetic field is by a factor of a few stronger than that in the minimum energy condition. The relation of the mid-infrared excess to the X-ray emission is briefly discussed.
The high-mass X-ray binary LS I +61{deg}303 exhibits variability in its radio and X-ray emissions, ranging from minute to hour time-scales. At such short time-scales, not much is known about the possible correlations between these two emissions from this source, which might offer hints to their origin. Here, we study the relationship between these emissions using simultaneous X-ray and radio monitoring. We present new radio observations using the Arcminute Microkelvin Imager Large Array telescope at two frequency bands, 13-15.5 and 15.5-18 GHz. We also describe new X-ray observations performed using the XMM-Newton telescope. These X-ray and radio observations overlapped for five hours. We find for the first time that the radio and X-ray emission are correlated up to 81 per cent with their few percent variability correlated up to 40 per cent. We discuss possible physical scenarios that produces the observed correlations and variability in the radio and X-ray emission of LS I +61{deg}303.
[Abridged] We report on deep, coordinated radio and X-ray observations of the black hole X-ray binary XTE J1118+480 in quiescence. The source was observed with the Karl G. Jansky Very Large Array for a total of 17.5 hrs at 5.3 GHz, yielding a 4.8 pm 1.4 microJy radio source at a position consistent with the binary system. At a distance of 1.7 kpc, this corresponds to an integrated radio luminosity between 4-8E+25 erg/s, depending on the spectral index. This is the lowest radio luminosity measured for any accreting black hole to date. Simultaneous observations with the Chandra X-ray Telescope detected XTE J1118+480 at 1.2E-14 erg/s/cm^2 (1-10 keV), corresponding to an Eddington ratio of ~4E-9 for a 7.5 solar mass black hole. Combining these new measurements with data from the 2005 and 2000 outbursts available in the literature, we find evidence for a relationship of the form ellr=alpha+beta*ellx (where ell denotes logarithmic luminosities), with beta=0.72pm0.09. XTE J1118+480 is thus the third system, together with GX339-4 and V404 Cyg, for which a tight, non-linear radio/X-ray correlation has been reported over more than 5 dex in ellx. We then perform a clustering and linear regression analysis on what is arguably the most up-to-date collection of coordinated radio and X-ray luminosity measurements from quiescent and hard state black hole X-ray binaries, including 24 systems. At variance with previous results, a two-cluster description is statistically preferred only for random errors <=0.3 dex in both ellr and ellx, a level which we argue can be easily reached when the known spectral shape/distance uncertainties and intrinsic variability are accounted for. A linear regression analysis performed on the whole data set returns a best-fitting slope beta=0.61pm0.03 and intrinsic scatter sigma_0=0.31pm 0.03 dex.
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